Injector driving apparatus

ABSTRACT

In an injector driving apparatus, a driving circuit supplies a current individually to each coil of multiple injectors, a current detection element detects the current flowing in a common current flow path, which is common to the coils, a current supply period guard part forcibly stops the current supplied from the driving circuit to the coil upon determination that a measured period reached a predetermined set period based on a detection result of the current detection element, and a diagnosis part operates in a period of no fuel injection to check whether the current supply period guard part normally stops the current supplied to the coil, by continuously supplying the current to the coil for only a short period, which disables the injector to open a valve, and sequentially switches over the coils.

CROSS REFERENCE TO RELATED APPLICATION

This application is based on Japanese patent application No. 2014-245126filed on Dec. 3, 2014, the disclosure of which is incorporated herein byreference.

FIELD

The present disclosure relates to an injector driving apparatus fordriving injectors.

BACKGROUND

One conventional injector for injecting fuel into an engine of a vehicleis electro-magnetically operated to open in response to supply of acurrent to a coil. In an injector driving apparatus for driving multipleinjectors, a selection switch is provided at a low-side (low-potentialside) of a coil of each injector to select a coil (injector to bedriven), to which a current is supplied. Thus, the current is suppliedto only the coil corresponding to the selection switch, which is turnedon, among multiple switches. In a case that the multiple injectors arenot driven for fuel injection at the same time, a current detectionelement is shared to detect the current supplied to each coil.Specifically, a resistor is provided as the current detection element ina current supply path, through which the current flows to the coils incommon (for example, JP 2007-205249 A).

In an engine control system for a vehicle, a power output of the engineis limited when an abnormality arises. One proposal is to provide aninjector driving apparatus with a current supply period guard function,which limits a time period of current supply to a coil of an injector toa predetermined period. With the limited period of current supply of thecoil, a quantity of fuel injected from the injector is limited and hencethe power output of the engine is limited. The current supply periodguard function specifically measures a period of continuous flow of thecurrent in the coil and, when the measured period reaches apredetermined period, forcibly stops the current supply to the coil.

If a current is simply supplied to the coil of the injector to diagnosewhether the current supply period guard function is normal or not, theinjector is driven to inject fuel unnecessarily.

SUMMARY

It is therefore an object to enable a diagnosis of a current supplyperiod guard function, which limits a current supply period to a coil ofan injector, in an injector driving apparatus without causing theinjector to inject fuel unnecessarily.

According to one aspect, an injector driving apparatus comprises adriving circuit, a common current flow path, a current detectionelement, a current supply period guard part and a diagnosis part, adriving circuit for supplying a current individually to coils ofmultiple injectors mounted on an engine of a vehicle. The common currentflow path allows the current to flow in the coils therethrough. Thecurrent detection element is provided in the common current flow pathfor detecting the current flowing in the common current flow path as acurrent, which flows to the coils. The current supply period guard partmeasures a period, during which the current continues to flow in thecommon current flow path, based on a detection result of the currentdetection element, and forcibly stops the current supplied from thedriving circuit to the coils when a measured period reaches apredetermined set period. The diagnosis part checks whether the currentsupply period guard part normally stops the current supplied from thedriving circuit to the coils, by supplying the current to each of thecoils for a period shorter than a minimum period, which enables theinjector to open a valve, and sequentially switches over the coilsthereby to continuously supply the current to the common current flowpath.

The diagnosis part performs a checking operation in a period of no fuelinjection into the engine.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram showing a configuration of an injectordriving apparatus according to a first embodiment;

FIG. 2 is a time chart showing an operation of fuel injection controlprocessing performed by a microcomputer in the first embodiment;

FIG. 3 is a flowchart showing guard function diagnosis processingperformed in the first embodiment;

FIG. 4 is a time chart showing an operation of the guard functiondiagnosis processing shown in FIG. 3;

FIG. 5 is a circuit diagram showing a configuration of an injectordriving apparatus according to a second embodiment; and

FIG. 6 is a flowchart showing guard function diagnosis processingperformed in the second embodiment.

EMBODIMENT

An electronic control unit, which is configured as an injector drivingapparatus, will be described below with reference to embodiments. In thefollowing description, the electronic control unit is referred to as anECU.

First Embodiment

An ECU 1 according to a first embodiment is configured as shown in FIG.1 to control fuel injection for an engine of a vehicle by drivingmultiple injectors mounted on the engine. The engine has four cylinders,for example. Although the injector is mounted on each cylinder of theengine, only two injectors 11 and 12 are exemplarily illustrated inFIG. 1. The injector 11 and the injector 12 are mounted on cylinders,into which fuel is not injected at the same time. The followingdescription is directed to driving of the injectors 11 and 12. Theinjectors 11 and 12 are operable electro-magnetically to open respectivevalves when respective inside coils 11 a and 12 a are supplied withcurrents.

As shown in FIG. 1, the ECU 1 includes a microcomputer 2 for centrallycontrolling operations of the ECU 1, a power circuit 3, a drivingcircuit 4 for driving the injectors 11 and 12, a driving control circuit5 for operating the driving circuit 4, and a current detection circuit 6and a current supply period guard circuit 7. The current detectioncircuit 6 and the current supply period guard circuit 7 are provided incommon for the injectors 11 and 12. The injectors 11 and 12 are drivento open respective valves in response to supply of currents to coils 11a and 12 a of the injectors 11 and 12, respectively.

The microcomputer 2 includes a CPU 21 for execution of programs, a ROM22 for storing the programs and fixed data, a RAM 23 for storing resultsof arithmetic operations of the CPU 21 and an A/D converter (ADC) 24.Although not illustrated, the microcomputer 2 further includes anon-volatile memory, which is capable of rewiring of data. As anoperation of the microcomputer 2, the CPU 21 executes the programsstored in the ROM 22.

A battery voltage VB, which is a positive-terminal voltage of a battery15 mounted in the vehicle, is supplied to a first power line 14 in theECU 1 through a main relay 16, which is provided as a power relay. Thebattery voltage VB is supplied to the first power line 14 also throughan ignition switch 17 and a diode 18. The ECU 1 is further provided witha relay driving switch 19, which turns on the main relay 16 in responseto a relay driving signal RD outputted from the microcomputer 2. In theECU 1, the power circuit 3 steps down the battery voltage VB suppliedfrom the first power line 14 and outputs a constant power voltage Vcc(for example, 5V), which the microcomputer 2 needs to operate.

When a vehicle user turns on the ignition switch 17, the power circuit 3outputs the power voltage Vcc to activate the microcomputer 2. Followingthe activation, the microcomputer 2 sets the relay driving signal RD toan active level (high level, for example) to turn on the relay drivingswitch 19 and the main relay 16. As a result, even when the ignitionswitch 17 is turned off after the activation of the microcomputer 2 bythe turn-on of the ignition switch 17, the battery voltage VB issupplied persistently to the first power line 14 through the main relay16 and hence the microcomputer 2 is maintained operable.

Upon determination that the ignition switch 17 is turned off, themicrocomputer 2 performs shut-down processing, which is to be finishedbefore stopping its operation and then sets the relay driving signal RDto an inactive level (low level, for example) to turn off the main relay16. Supply of the battery voltage VB to the first power line 14 is shutdown so that the microcomputer 2 does not operate.

Although not shown, a signal indicating an on/off state of the ignitionswitch 17 (IGSW signal) is inputted to the microcomputer 2 through aninput circuit. The microcomputer 2 is thus enabled to check whether theignition switch 17 is in the on-state or the off-state based on the IGSWsignal. As a modification, the relay driving switch 19 may be configuredto turn on as a result of an OR logic between the relay driving signalRD from the microcomputer 2 and the IGSW signal. In this modification, adiode 18 need not be provided.

The driving circuit 4 includes a current output line 40, a firstselection switch 41 and a second selection switch 42. The current outputline 40 is connected to the coils 11 a and 12 a of the injectors 11 and12 at high-potential ends, which are connected in common. One outputterminal of the first selection switch 41 is connected to alow-potential end of the coil 11 a. One output terminal of the secondselection switch 42 is connected to a low-potential end of the coil 12a. The low-potential ends of the coils 11 a and 12 a are opposite to thecurrent output line 40 side (high-potential ends) of the coils 11 a and12 a. The other output terminal of the first selection switch 41, whichis opposite to the coil 11 a side, and the other output terminal of thesecond selection switch 42, which is opposite to the coil 12 a side, areconnected to a ground line of 0V through a current detection resistor 61described below.

The driving circuit 4 further includes a first high-side switch 43 and asecond high-side switch 44, which are provided at high potential endsides of the coils 22 a and 12 a. One output terminal of the firsthigh-side switch 43 is connected to the first power line 14, whichsupplies the battery voltage VB. One output terminal of the secondhigh-side switch 44 is connected to a second power line 20 in the ECU 1.The other output terminal of the second high-side switch 44 is connectedto the current output line 40. A boosted voltage VU, which is an outputvoltage of a voltage booster circuit (not shown), is supplied to thesecond power line 20. Although not illustrated, the voltage boostercircuit is a voltage-boosting type DC/DC converter, which charges acapacitor by stepping up the battery voltage VB of the first power line14. A charge voltage of the capacitor is the boosted voltage VU (50V,for example) higher than the battery voltage VB.

The driving circuit 4 further includes a diode 45 for blocking a currentfrom flowing in reverse and a diode 46 for fly-wheeling a current. Ananode of the diode 45 is connected to the other output terminal of thefirst high-side switch 43, which is opposite to the first power line 14side. A cathode of the diode 45 is connected to the current output powerline 40. An anode of the diode 46 is connected to the ground line and acathode of the diode 46 is connected to the power output line 40.

The current detection circuit 6 includes an amplifier circuit 62 inaddition to the current detection resistor 61. One end of the currentdetection resistor 61 is connected in common to the output terminal ofthe first selection switch 41, which is opposite to the coil 11 a side,and the output terminal of the second selection switch 42, which isopposite to the coil 12 a side. The other end of the current detectionresistor 61 is connected to the ground line.

That is, a current flow path between a node 63, at which the outputterminals of the first selection switch 41 and the second selectionswitch 42 opposite to the coils 11 a and 12 a sides are connected, andthe ground line form a common current flow path 64, which allowscurrents i1 and i2 of the coils 11 a and 12 a to flow. The currentdetection resistor 61 is provided in the common current flow path 64.The current detection resistor 61 is thus a part of the common currentflow path 64. The current i1 flows in the coil 11 a through the firstselection switch 41. The current i2 flows in the coil 12 a through thesecond selection switch 42.

The amplifier circuit 62 amplifies a difference between voltages at bothends of the current detection resistor 61 and outputs an amplifiedvoltage signal as a current detection signal Vi, which indicates acurrent flowing in the coil 11 a or 12 a (current flowing in the commoncurrent flow path 64). The current detection signal Vi, whichcorresponds to a detection result of the current detection resistor 6,is inputted to the microcomputer 2 and the current supply period guardcircuit 7.

The current supply period guard circuit 7 includes a comparator circuit71, a check circuit 72, an AND circuit 73 and a memory 74. Thecomparator circuit 71 compares the current detection signal Vi of thecurrent detection circuit 6 with a threshold signal Vth, which is avoltage signal. The comparison circuit 71 outputs a high-level signaland a low-level signal when the current detection signal Vi is equal toor higher than the threshold signal Vth and lower than the thresholdsignal Vth, respectively. The output signal of the comparator circuit 71is inputted to the AND circuit 73 and also to the microcomputer 2 as adiagnosis signal Di.

The AND circuit 73 outputs the output signal of the comparator circuit71 to the check part 72 without change when a current supply guardsetting signal Sg of the microcomputer 2 has a level (high level, forexample), which makes the function of the current supply period guardcircuit 7 effective. The AND circuit 73 maintains the output signal tothe check part 72 at the other level (low level, for example), whichmakes the function of the current supply period guard circuit 7ineffective.

The check part 72 measures a period, during which the output signal ofthe AND circuit 73 continues to be at the high level. When a measuredperiod reaches a guard period Tg stored in the memory 74, the check part72 sets a forced-off command signal Soff, which is inputted to thedriving control circuit 5, to a low level. The guard period Tg is apredetermined set period. The forced-off command signal Soff is alow-active signal, which indicates forcibly stopping the current supplyfrom the driving circuit 4 to the coils 11 a and 12 a. When the measuredperiod does not reach the guard period Tg stored in the memory 74 or thecurrent supply guard setting signal Sg is at the low level, the checkpart 72 sets the forced-off command signal Soff, which is inputted tothe driving control circuit 5, to a high level.

When the current supply guard setting signal Sg is at the high level, acurrent equal to or higher than a fixed value Ith continues to flow ineither of the coils 11 a and 12 a as long as the output signal of theAND circuit 73 continues to be at the high level. The fixed value Ithcorresponds to a voltage value corresponding to the threshold signalVth, which the comparator circuit 71 uses. Specifically, assuming thatthe current detection resistor 61 has a resistance value R and theamplifier circuit 62 has an amplification gain G, the fixed value isdefined as follows.

Ith=Vth/(R×G)

For this reason, the current detection circuit 6 operates when thecurrent supply guard setting signal Sg from the microcomputer 2 is atthe high level and measures the period of continuous flow of the currentin the coil 11 a or 12 a based on the current detection signal Vi of thecurrent detection circuit 6. When the measured period reaches the guardperiod Tg, the current supply period guard circuit 7 changes theforced-off command signal Soff from the high level to the low level.

The guard period Tg in the memory 74 is set for the current supplyperiod guard circuit 7 and is variable with data from the microcomputer2. The guard period Tg is not limited to a variable value but may be afixed value.

The forced-off command signal Soff is inputted to the driving controlcircuit 5 from the current supply period guard circuit 7 as describedabove. Further, a boosted-voltage application signal HU, a batteryvoltage application signal HB, a first low-side driving signal LD1, asecond low-side driving signal LD2 and a current supply prohibitionsignal Sde are inputted to the driving control circuit 5 from themicrocomputer 2.

The boosted-voltage application signal HU is a command signal, which ishigh-active, for turning on the second high-side switch 44 to supply theboosted voltage VU to the ends of the coils 11 a and 12 a at the highpotential side. The battery voltage application signal HB is a commandsignal, which is also high-active, for turning on the first high-sideswitch 43 to supply the battery voltage VB to the ends of the coils 11 aand 12 a at the high potential side. The first low-side driving signalLD1 is a command signal, which is high-active, for turning on the firstselection switch 41 to supply the current to the coil 11 a. The secondlow-side driving signal LD2 is a command signal, which is high-active,for turning on the second selection switch 42 to supply the current tothe coil 12 a. The current supply prohibition signal Sde is a commandsignal, which is low-active similarly to the forced-off command signalSoff, for forcibly stopping the current supply to the coils 11 a and 12a.

The driving control circuit 5 includes AND circuits 51 to 58. The ANDcircuit 51 outputs a logical-product signal of the boosted-voltageapplication signal HU and the forced-off command signal Soff. The ANDcircuit 52 turns on the second high-side switch 44 when both of theoutput signal of the AND circuit 51 and the current supply prohibitionsignal Sde are at the high levels. The AND circuit 52 turns off thesecond high-side switch 44 when at least one of the output signals ofthe AND circuit 51 and the current supply prohibition signal Sde is atthe low level.

The AND circuit 53 outputs a logical-product signal of the batteryvoltage application signal HB and the forced-off command signal Soff.The AND circuit 54 turns on the first high-side switch 43 when both ofthe output signal of the AND circuit 53 and the current supplyprohibition signal Sde are at the high levels. The AND circuit 54 turnsoff the first high-side switch 43 when at least one of the outputsignals of the AND circuit 53 and the current supply prohibition signalSde is at the low level. The AND circuit 55 outputs a logical-productsignal of the first low-side driving signal LD1 and the forced-offcommand signal Soff. The AND circuit 56 turns on the first selectionswitch 41 when both of the output signal of the AND circuit 55 and thecurrent supply prohibition signal Sde are at the high levels. The ANDcircuit 56 turns off the first selection switch 41 when at least one ofthe output signals of the AND circuit 55 and the current supplyprohibition signal Sde is at the low level.

The AND circuit 57 outputs a logical-product signal of the secondlow-side driving signal LD2 and the forced-off command signal Soff. TheAND circuit 58 turns on the second selection switch 42 when both of theoutput signal of the AND circuit 57 and the current supply prohibitionsignal Sde are at the high levels. The AND circuit 58 turns off thesecond selection switch 42 when at least one of the output signals ofthe AND circuit 57 and the current supply prohibition signal Sde is atthe low level.

When both of the forced-off command signal Soff and the current supplyprohibition signal Sde are at the high levels, the driving controlcircuit 5 turns on/off the second high-side switch 44 in response to thehigh/low level of the boosted-voltage application signal HU and turnson/off the first high-side switch 43 in response to the high/low levelof the battery voltage application signal HB. Similarly, when both ofthe forced-off command signal Soff and the current supply prohibitionsignal Sde are at the high levels, the driving control circuit 5 turnson/off the first selection switch 41 in response to the high/low levelof the signal LD and turns on/off the second selection switch 42 inresponse to the high/low level of the second low-side driving signalLD2. On the other hand, when at least one of the forced-off commandsignal Soff and the current supply prohibition signal Sde is at the lowlevel, the driving control circuit 5 forcibly turns off all the switches41 to 44 in the driving circuit 4 irrespective of the signals HU, HB,LD1 and LD2 outputted from the microcomputer 2.

Processing of the microcomputer 2 will be described next.

(Fuel Injection Control Processing)

The microcomputer 2 calculates a start timing of fuel injection and aquantity of fuel injection for each cylinder based on an engine rotationspeed, accelerator position varied by a vehicle driver and the like, andthen calculates a driving period of each injector 11, 12 based on suchcalculation results. As the driving period of the injector, themicrocomputer 2 calculates a start timing of current supply to the coilof the injector and a period of current supply to the coil of theinjector. In normal time, the microcomputer 2 sets the current supplyprohibition signal Sde for the driving control circuit 5 to the highlevel and sets the current supply guard setting signal Sg for thecurrent supply period guard circuit 7 to the low level. Thus, both ofthe forced-off command signal Soff and the current supply prohibitionsignal Sde outputted to the driving control circuit 5 are at the lowlevels.

Driving of the injector 11 will be described below as one representativeexample among multiple injectors for multiple cylinders. As shown inFIG. 2, the microcomputer 2 sets the first low-side driving signal LD1to the high level (indicated as H in FIG. 2) and turns on the firstselection switch 41 during the driving period of the injector 11.Further, the microcomputer 2 sets the boosted-voltage application signalHU to the high level and turns on the second high-side switch 44 at thestart time of the driving period of the injector 11 (that is, at starttiming of current supply to the coil 11 a).

Thus the first selection switch 41 turns on with the boosted voltage VUbeing applied to the high-side end part of the coil 11 a. The currentsupply to the coil 11 a is started with the boosted voltage VH as apower supply. In this case, the capacitor discharges to the coil 11 a.

During the driving period of the injector 11, the microcomputer 2detects the current i1 flowing in the coil 11 a by ND-converting thecurrent detection signal Vi outputted from the current detection circuit6. When the microcomputer 2 detects that the current i1 reached a targetmaximum value IP of the current supply start time after setting of theboosted-voltage application signal HU to the high level, themicrocomputer 2 sets the boosted-voltage application signal HU to thelow level (indicated as L in FIG. 2) and turns off the second high-sideswitch 44. By supplying the boosted voltage VU higher than the batteryvoltage VB as the power supply source and thereby supplying the currentto the coil 11 a at the start time of the current supply, avalve-opening response of the injector 11 is speeded up. Themicrocomputer 2 may set the boosted-voltage application signal HU foronly a fixed period.

After setting the boosted-voltage application signal HU at the lowlevel, the microcomputer 2 performs constant current control by turningon and off the first high-side switch 43 so that the current i1 isregulated to a fixed current lower than the target maximum value IP. Forexample, the microcomputer 2 sets the battery voltage application signalHB to the high level and turns on the first high-side switch 43 bydetecting that the current i1 fell to a low-side threshold value IL. Themicrocomputer 2 sets the battery voltage application signal HB to thelow level and turns off the first high-side switch 43 by detecting thatthe current i1 rose to a high-side threshold value IH (>IL). When thefirst high-side switch 43 turns on, the current flows to the coil 11 awith the battery voltage VB of the first power line 14 as the powersupply source. When the first high-side switch 43 turns off, the currentflywheels to the coil 11 a from the ground line through the diode 46.

Then the microcomputer 2 sets the first low-side driving signal LD1 tothe low level and turns off the first selection switch 41 at the endtime of the driving period of the injector 11. The microcomputer 2 setsthe battery voltage application signal HB to the low level and turns offthe first high-side switch 43. Thus the current supply to the coil 11 ais stopped and the valve of the injector 11 closes. For driving theinjector 12, the second low-side driving signal LD2 is set to the highlevel in place of setting the first low-side driving signal LD1 to thehigh level.

<Engine Power Output Limitation Processing>

When the microcomputer 2 detects an abnormality such as an abnormalityin a monitor circuit for checking whether the microcomputer 2 is normalor not or an abnormality in a function of controlling a throttle of theengine, which will possibly cause the engine to produce an excessivepower output, the microcomputer 2 causes the current supply period guardcircuit 7 to perform its limiting function. Specifically, themicrocomputer 2 sets the guard period Tg for the current supply periodguard circuit 7 and sets the current supply guard setting signal Sg forthe current supply period guard circuit 7 to the high level.

When the current supply guard setting signal Sg becomes the high level,the current supply period guard circuit 7 measures the period ofcontinuous flow of current in the coil 11 a or 12 a. When the measuredperiod reaches the guard period Tg, the current supply period guardcircuit 7 sets the forced-off command signal Soff to the low level.

When the forced-off command signal Soff changes to the low level, thedriving control circuit 5 forcibly turns off all the switches 41 to 44in the circuit 4. Thus the current supply from the circuit 4 to thecoils 11 a and 11 b is forcibly stopped.

When the current supply period guard circuit 7 performs its function,the current supply period for the coils 11 a and 12 a is limited to theguard period Tg. As a result, the quantity of fuel injection from theinjectors 11 and 12 is limited and the power output of the engine islimited. Safety of a vehicle is thus improved.

The microcomputer 2 has a higher reliability in its hardware andsoftware (collectively referred to as resource) provided for performingthe output limitation processing than in its other resource provided forperforming the fuel injection control processing.

(Guard Function Diagnosis Processing)

The microcomputer 2 further performs guard function diagnosis processingfor checking whether the function of the guard circuit 7 is normal ornot.

In FIG. 1, the diagnosis function part 26 illustrated inside themicrocomputer 2 corresponds to a resource, which is for performing theguard function diagnosis processing, among resources of themicrocomputer 2. The diagnosis function part 26 is ensured to have itsreliability level equal to or higher than that of the resource, whichperforms the engine power output limitation processing.

The microcomputer 2 performs the guard function diagnosis processingshown in FIG. 3 in each of the following periods <1> to <4>, in which nofuel injection into the engine is performed.

<1> Period from a turn-off of the ignition switch 17 to an end of powersupply to the ECU 1, that is, until main the relay 1 is turned off.

In this case, the microcomputer 2 performs the guard function diagnosisprocessing shown in FIG. 3 as a part of the shutdown processing.

<2> Period from a turn-on of the ignition switch 17 to a start of theengine, that is, cranking by a starter.

<3> Period of automatic stop of the engine by idle-stop control.

The idle-stop control automatically stops the engine when apredetermined automatic stop condition is satisfied in the course ofengine operation and then automatically restarts the engine when apredetermined automatic restart condition is satisfied. This idle-stopcontrol processing may be performed by the microcomputer 2 in the ECU 1or a microcomputer in other ECUs.

<4> Period of fuel shut-off for the engine upon deceleration of thevehicle.

The fuel shut-off prohibits the fuel injection from the injector. Themicrocomputer 2 performs fuel shut-off control processing as well.According to the fuel shut-off control processing, the injector isprohibited from injecting fuel, when an accelerator is not operated atall by a driver and a vehicle speed is higher than a predeterminedvalue, for example.

As shown in FIG. 3, the microcomputer 2 causes the current supply periodguard circuit 7 to perform its period guard function at S110 afterstarting the guard function diagnosis processing. Specifically, themicrocomputer 2 sets the guard period Tg for the current supply periodguard circuit 7 and sets the current supply guard setting signal Sg tothe high level. In a case that the guard period Tg need not be variedfor diagnosing the function of the current supply period guard circuit7, the microcomputer 2 may only set the current supply guard settingsignal Sg to the high level as S110.

The microcomputer 2 then starts at next S120 continuous short-perioddriving control, which is indicated as continuous short driving controlor continuous control or similar abbreviated form in the figures. Hereit is noted that a minimum value of a period of current supply to thecoil 11 a, 12 a for enabling the injector 11, 12 to open its valve forfuel injection is referred to as a valve-opening minimum period.

The continuous short-period driving control is for performing acontinuous supply of a current to the common current flow path 64 bycausing the driving circuit 4 to supply the current to the coil 11 a, 12a for only a fixed period Ts, which is shorter than the valve-openingminimum period, and switching over the coils sequentially, to which thecurrent is supplied for only the fixed period Ts.

Specifically, as shown in FIG. 4, the microcomputer 2 sets the batteryvoltage application signal HB to the high level and turns on the firsthigh-side switch 43 as the continuous short-period driving control.Further, as the continuous short-period driving control, themicrocomputer 2 sets the first low-side driving signal LD1 and thesecond low-side driving signal LD2 to the high level for the fixedperiod Ts alternately thereby to turn on the first selection switch 41and the second selection switch 42 for the fixed period Ts alternately.Thus, while limiting the fuel injection quantity of the injectors 11 and12 to be 0 (that is, disabling fuel injection from the injectors 11 and12), the current is continuously supplied to the common current flowpath 64.

In FIG. 4, the injection by the first injector and the injection by thesecond injector are the quantity of fuel injection from the injector 11and the quantity of fuel injection from the injector 12, respectively.In FIG. 4 and the following description, the detection current is thecurrent i1, i2 detected by the current detection circuit 6 and thecurrent, which flows in the common current flow path 64. In thecontinuous short-period driving control, the boosted-voltage applicationsignal HU may be set to the high level to turn on the second high-sideswitch 44 in place of setting the battery voltage application signal HBto the high level. Further, in the continuous short-period drivingcontrol, both of the battery voltage application signal HB and theboosted-voltage application signal HU may be set to the high levels,respectively.

Referring back to FIG. 3, the microcomputer 2 waits for an elapse of apredetermined period at next S130 after starting the continuousshort-period driving control at S120. The predetermined period providedfor waiting at S130 is set to be equal to or slightly longer than aperiod Td1 (refer to FIG. 4), which is a period from when the continuousshort-period driving control is started to when the detection currentreaches the fixed value Ith and the diagnosis signal Di is set to thehigh level.

After waiting for the predetermined period at S130, the microcomputer 2checks at S140 whether the diagnosis signal Di outputted from thecomparator circuit 71 is at the high level. When the diagnosis signal Diis at the high level, the microcomputer 2 performs S150.

The microcomputer 2 checks at S150 whether a continuous control period Tof performing the continuous short-period driving control (that is,elapse of time from starting the continuous short-period drivingcontrol) reached an abnormality determination period Tj, which isindicated as an abnormality period Tj in the figures.

It is assumed here that, as shown in FIG. 4, that the forced-off commandsignal Soff outputted from the current supply period guard circuit 7changes to the low level in the course of performing the continuousshort-period driving control. In FIG. 4, a period Td2 indicates a periodfrom when the forced-off command signal Soff changes to the low-level towhen the detection current falls to the fixed value Ith and thediagnosis signal to the microcomputer 2 becomes the low level. Theabnormality determination period Tj is set to be slightly longer than asum of the guard period Tg in the current supply period guard circuit 7and the periods Td1 and Td2.

Referring back to FIG. 3, when the microcomputer 2 determines at S150that the elapse of time of performing the continuous short-perioddriving control does not reach the abnormality determination period Tj,the microcomputer 2 performs S140 again. When the microcomputer 2determines at S150 that the elapse of time of performing the continuousshort-period driving control reached the abnormality determinationperiod Tj, the microcomputer 2 determines at S160 that the function ofthe current supply period guard circuit 7 is abnormal (that is, circuit7 is not operating normally).

That is, the microcomputer 2 performs S160 following S150 in a casethat, even when the abnormality determination period Tj elapses afterstarting of the continuous short-period driving control, the forced-offcommand signal Soff outputted from the current supply period guardcircuit 7 does not change to the low level and the diagnosis signal Diremains at the high level. That is, although the common current flowpath 64 is supplied with the current continuously for the abnormalitydetermination period Tj, which is longer than the guard period Tg, thecurrent supply period guard circuit 7 fails to stop the current supplyfrom the circuit 4 to the coils 11 a and 12 a. In this case, themicrocomputer 2 determines that the function of the current supplyperiod guard circuit 7 is abnormal.

The microcomputer 2 thus stops the continuous short-period drivingcontrol at next S170. Specifically, the microcomputer 2 changes thebattery voltage application signal HB, which has been set to the highlevel, to the low level and further maintains the first low-side drivingsignal LD1 and the LD2, which have been set to the high/low levels, tobe at the low levels. The microcomputer 2 then performs thepredetermined fail-safe processing at S180 and finishes the guardfunction diagnosis processing.

When the microcomputer 2 determines at S140 that the diagnosis signal Diis not at the high level (that is, at the low level), the microcomputer2 performs S190. The microcomputer 2 performs S190 following S140, whenthe diagnosis signal Di becomes the low level normally as a result ofsetting the forced-off command signal Soff to the low level by thecurrent supply period guard circuit 7 and prohibiting the circuit 4 fromsupplying the current to the coil 11 a and 12 a. The microcomputer 2thus determines that the function of the guard circuit 7 is normal. Itis noted that FIG. 4 shows a case that the function of the currentsupply period guard circuit 7 is normal. The microcomputer 2 then stopsthe continuous short-period driving control at S200 and finishes theguard function diagnosis processing.

In any of cases that the microcomputer 2 determines that the function ofthe current supply period guard circuit 7 is abnormal at S160 and normalat S190, the current is supplied to the common current flow path 64 bythe continuous short-period driving control for a period longer than theguard period Tg.

<Fail-Safe Processing>

The fail-safe processing, which the microcomputer 2 performs at S180 inthe guard function diagnosis processing, will be described next.

The microcomputer 2 performs the following <FS1> as the fail-safeprocessing at S180 of the guard function diagnosis processing performedin the period <1>.

<FS1> The microcomputer 2 stores abnormality information indicating adetermination of abnormality at S160 in a non-volatile memory, forexample. The microcomputer 2 performs abnormality notificationprocessing, which notifies a vehicle user of an occurrence ofabnormality, and starting prohibition processing, which prohibitsstarting of the engine, when the above-described abnormality informationis stored in the non-volatile memory at the time of next activation ofthe microcomputer 2 as a result of next turn-on of the ignition switch17.

As the abnormality notification processing, for example, an alarm lightmay be activated to indicate an occurrence of abnormality, a displaydevice may be activated to display a message of an occurrence ofabnormality or a sound device may be activated to generate a voicemessage indicating an occurrence of abnormality. As the startingprohibition processing, for example, current supply to the starter maybe prohibited or fuel injection from the injectors 11 and 12 may beprohibited by setting the current supply prohibition signal Sdeoutputted to the driving control circuit 5 to the low level.

Since the vehicle is assumed to be parked at a safe place during theperiod <1>, the fail-safe processing for stopping the engine startingperformed in <FS1> is considered to be preferred from the standpoint ofsafety.

The microcomputer 2 performs the following processing <FS2> as thefail-safe processing at S180 in the guard function diagnosis processingperformed during the period <2>.

<FS2> The microcomputer 2 performs the abnormality notificationprocessing and the starting prohibition processing described above.

Since the vehicle is assumed to be parked at a safe place during theperiod <2> as well, the fail-safe processing for stopping the enginestarting performed in <FS2> is considered to be preferred from thestandpoint of safety.

The microcomputer 2 performs the following processing <FS3, FS4> as thefail-safe processing at S180 during the guard function diagnosisprocessing performed during the period <3> or <4>.

<FS3, FS4> The microcomputer 2 performs the abnormality notificationprocessing described above and transfer request processing forrequesting a vehicle user (driver) to transfer the vehicle to a safeplace as a limp-home operation. Further, the microcomputer 2 performsthe injection prohibition processing for prohibiting the fuel injectioninto the engine after an elapse of a fixed period, for example.

As the transfer request processing, a message requesting a transfer to asafe place may be displayed on a display device or outputted from asound device. In parallel with the transfer request processing, theengine power output limiting processing may be performed by controllingan open angle of an electronic throttle. As the injection prohibitionprocessing, for example, the current supply prohibition signal Sdeoutputted to the driving control circuit 5 may be set to the low level.

In the periods <3> and <4>, the vehicle is assumed to be on a road. Forthis reason, by performing the fail-safe processing <FS3, FS4> describedabove, the vehicle user is allowed to move the vehicle to the safe placeduring the period, in which the fuel injection is not prohibited.

<Advantage>

The microcomputer 2 of the ECU 1 performs the continuous short-perioddriving control in the guard function diagnosis processing shown in FIG.3 thereby to allow the current to flow in the common current flow path64 for the period longer than the guard period Tg without causing thefuel injection from the injectors 11 and 12. The microcomputer 2 thuschecks at S140 and S150 shown in FIG. 3 whether the current supplyperiod guard circuit 7 normally causes the diving circuit 4 to stop thecurrent supply to the coils 11 a and 12 a. Further the microcomputer 2performs the guard function diagnosis processing of FIG. 3 in theperiod, during which no fuel is injected into the engine.

For this reason, according to the ECU 1, it is possible to diagnosewhether the function of the current supply period guard circuit 7 isnormal without affecting the normal fuel injection control for theengine and without causing the injectors 11 and 12 to inject fuelactually and unnecessarily.

Further, the microcomputer 2 determines that the function of the currentsupply period guard circuit 7 is abnormal (S150: YES and S160), when thecurrent supply to the coil 11 a and 12 a is not stopped in spite of thecontinuous supply of current to the common current flow path 64 by thecontinuous short-period driving control for the abnormalitydetermination period Tj, which is longer than the guard period Tg. It isthus possible to determine abnormality and normality correctly.

The microcomputer 2 performs the guard function diagnosis processing inthe period, during which the ignition switch 17 is in the off-state, inthe period <1> described above. In the period, during which the ignitionswitch 17 is in the off-state, load-driving noise is rarely generated ornot generated at all. For this reason, the microcomputer 2 can diagnosethe function of the current supply period guard circuit 7 correctlywithout being affected by the noise, which is generated in drivingelectric loads other than the injector.

Since the microcomputer 2 performs the guard function diagnosisprocessing before starting the engine cranking in the period <2>, it ispossible to prohibit starting of the engine. It is thus possible toprevent a vehicle from being moved under a state that a safety functionprovided by the current supply period guard circuit 7 is not secured.

Since the microcomputer 2 performs the guard function diagnosisprocessing in the period <3> or <4>, the microcomputer 2 can detect anabnormality even when the function of the current supply period guardcircuit 7 becomes abnormal in one trip of a vehicle, which is fromstarting to stopping of the engine.

The microcomputer 2 is not limited to perform the guard functiondiagnosis processing in all of the periods <1> to <4>. The microcomputer2 may alternatively be configured to perform the guard diagnosis in atleast one of the periods <1> to <4>.

Second Embodiment

An ECU according to a second embodiment will be described next. Samestructural components and processing as those of the first embodimentare designated with the same reference numerals thereby to simplify thedescription.

An ECU 9 according to the second embodiment shown in FIG. 6 is differentfrom the ECU 1 of the first embodiment in the following points <a> to<c>.

<a> The current supply period guard circuit 7 is not provided in ahardware configuration.

The current detection signal Vi outputted from the current detectioncircuit 6 is inputted to the microcomputer 2 as the signal Di.

<b> The microcomputer 2 performs the current supply period guardprocessing for performing the same function (current supply period guardfunction) of the current supply period guard circuit 7 by software. Themicrocomputer 2 therefore performs the current supply period guardfunction of the microcomputer 2 in the engine power output limitationprocessing without performing the function of the current supply periodguard circuit 7 upon detection of the abnormality that the engine islikely to produce excessive output. Specifically, the microcomputer 2performs an internal setting for permitting the performance of thecurrent supply period guard processing in place of setting the currentsupply guard setting signal Sg for the current supply period guardcircuit 7 to the high level. Further, the microcomputer 2 sets the guardperiod Tg in a memory area (referred to as a guard period memory area)of the RAM 23, in which the guard period Tg is stored to be referred toin the current supply period guard processing, for example, in place ofsetting the guard period Tg relative to the current supply period guardcircuit 7.

In the current supply period guard processing, the microcomputer 2A/D-converts the inputted diagnosis signal Di and checks whether thediagnosis signal Di is equal to or higher than the threshold signal Vth.The microcomputer 2 then measures a period, during which the diagnosissignal Di continues to be equal to or higher than the threshold signalVth. When a measured period of continuation reaches a set guard periodTg, the microcomputer 2 sets the forced-off command signal Soff for Thedriving control circuit 5 to the low level. When the forced-off commandsignal Soff outputted from the microcomputer 2 to the driving controlcircuit 5 changes to the low level, the current supply to the coils 11 aand 12 a are forcibly stopped as in the first embodiment.

In FIG. 5, the guard function part 27 illustrated inside themicrocomputer 2 indicates a resource for performing the current supplyperiod guard processing (that is, a resource for performing a currentsupply period guard function) among resources of the microcomputer 2.The reliability level of the guard function part 27 is higher than thatof the fuel injection control processing. For example, it is as high asthat of the resource for performing the engine power output limitationprocessing.

<c> The microcomputer 2 performs the guard function diagnosis processingshown in FIG. 6 in place of the guard function diagnosis processingshown in FIG. 3. The guard function diagnosis processing shown in FIG. 6is different from the guard function diagnosis processing shown in FIG.3 in that S115 and S145 are provided in place of S110 and S140,respectively.

The microcomputer 2 performs the current supply period guard function ofthe microcomputer 2 at S115. Specifically, the microcomputer 2 sets theguard period Tg in the guard period memory area of the RAM 23 andperforms the internal setting for permitting performance of the currentsupply period guard processing.

The microcomputer 2 checks at S145 whether the current detection signalVi outputted from the current detection circuit 6 is equal to or higherthan the threshold signal Vth. This checking at S145 is substantiallythe same as checking whether the signal Di is at the high level at S140in FIG. 3. The microcomputer 2 performs S150 upon determination that Diis equal to or higher than Vth at S145. The microcomputer 2 performsS190 upon determination that Di is not equal to nor higher than Vth(that is, Di is lower than Vth) at S145.

The ECU 9 according to the second embodiment also provides the similaradvantage as those of the ECU 1 of the first embodiment. Since the ECU 9is not provided with the current supply period guard circuit 7 incomparison to the ECU 1, the number of hardware structural componentsmay be reduced.

The injector driving apparatus is not limited to the embodimentsdescribed above, but may be implemented differently. The numbers andnumerical values described above are only exemplary and may be othervalues. For example, the number of injectors, which are common to thecurrent detection circuit 6, is not limited to 2 but may be equal to orlarger than 3. The function of the guard function diagnosis processingmay be realized by a hardware circuit, which is separate from themicrocomputer 2.

What is claimed is:
 1. An injector driving apparatus comprising: adriving circuit for supplying a current individually to coils ofmultiple injectors mounted on an engine of a vehicle; a common currentflow path, in which the current flows to the coils in common; a currentdetection element provided in the common current flow path for detectingthe current flowing in the common current flow path as a current, whichflows to the coils; a current supply period guard part for measuring aperiod, during which the current continues to flow in the common currentflow path, based on a detection result of the current detection element,and forcibly stopping the current supplied from the driving circuit tothe coils when a measured period reaches a predetermined set period; anda diagnosis part for checking whether the current supply period guardpart normally stops the current supplied from the driving circuit to thecoils, by supplying the current to each of the coils for a periodshorter than a minimum period, which enables the injector to open avalve, and sequentially switching over the coils thereby to continuouslysupply the current to the common current flow path, wherein thediagnosis part performs a checking operation in a period of no fuelinjection into the engine.
 2. The injector driving apparatus accordingto claim 1, wherein: the diagnosis part determines that the currentsupply period guard part is abnormal when the current is not stoppedfrom being supplied to the coil even in a case of a continuous currentsupply to the common current flow path for only a period longer than theset period.
 3. The injector driving apparatus according to claim 1,wherein: the diagnosis part operates in a period, during which power issupplied to the injector driving apparatus after an ignition switch ofthe vehicle is turned off.
 4. The injector driving apparatus accordingto claim 1, wherein: the diagnosis part operates in a period from whenan ignition switch of the vehicle is turned on to when an enginecranking is started.
 5. The injector driving apparatus according toclaim 1, wherein: the diagnosis means operates in a period, during whichthe engine is automatically stopped under an idle-stop control.
 6. Theinjector driving apparatus according to claim 1, wherein: the diagnosispart operates in a period, during which fuel injection to the engine isshut off upon deceleration of the vehicle.